There's something in the air at the Royal Court. Jerusalem, Jez Butterworth's brilliantly mischievous requiem for rural England, is a stinker. Literally. As Susannah Clapp observed, "At times, you can actually smell the action onstage."

Stepping into the auditorium is to swap the exhaust fumes of Sloane Square for something altogether easier on the alveoli. A dewy freshness lingers, tinged with a faint bonfire-like smokiness that tickles at your nostril hairs. When two tattooed heavies wielding branding rods burst into a mobile home, a stench suggesting scorching flesh soon follows. This is later interrupted by the pungency of petrol, as Mark Rylance's Rooster Byron liberally douses the vehicle. It's a smart device from director Ian Rickson, cunningly echoing Butterworth's focus on the inorganic invasion of all that is green and pleasant.

However, each new smell wafting off the stage succeeded in breaking my concentration. Smell always marks an intrusion (or should that be infusion?) of reality; it charges at us and refuses to be ignored. In our everyday lives, we read smell in terms of cause and effect: it points towards whatever produces it. When an odour curls up our nostrils in the theatre, we can't help but question its source. The problem is that this draws attention either to the simulation of the smell or, when confirmed as genuine, the pretence that surrounds it.

In Jerusalem, we know that the aromas don't stem from the sources suggested on stage. After all, health and safety laws simply won't allow Rylance to marinade the stage in petrol; we can't help but become aware of the trickery at play. The same is true of the chemical scents that accompany stage haze and pyrotechnics, which highlight their own fakery by seeming too sterile and synthetic. Nothing is quite as disruptive as the oddly fishy pong that seems to curdle the air when a fake cigarette is smoked on the stage. The sensory information received is too dislocated: our nose is at odds with our eyes.

Even when we can match a smell to its source, as Aleks Sierz recently did during the Chinese takeaway scoffed down in Apologia at the Bush, we are reminded that the food being eaten is more real than those characters eating it. An audience will always sniff out the truth.